1. E.E.Dept. head, University of Rome “Tor Vergata”, Rome, Italy
HEMTs in Europe (GaAs HEMT low-noise technologies, design techniques, characterization and modeling)
Ernesto Limiti
E.E.Dept. head, University of Rome “Tor Vergata”, Rome, Italy

2. Who and Where we are University of Roma “Tor Vergata”
Founded in 1982
600 hectares of Campus
6 Faculties & 35k students
Electronic Engineering Department
Founded in 1983
150 people
MiMEG Group
2 Full & 3 Associate Prof.
5 Researchers
1 Technicians
5 PhD Students
3 Post Docs

3. Methodologies & Designs
What we do at MiMEG
Methodologies & Designs
Modelling
Characterization
Small-Signal
Large-Signal
Noise
Time Domain
Small-Signal
(bias-dependent, scalable)
Noise
Large-Signal
High-Efficiency Power Amplification & Linearization Techniques
Linear Amplification (Gain blocks, LNA …)
Nonlinear functionalities (MIXER, Multipliers, Dividers, VCO…)
Advanced Functions (Core Chip, DigiPS, DigiATT)
MMIC and MIC Subsystem Integration (SCFE, Tx/Rx modules)
From 250kHz up to 120 GHz (extending to 300GHz) and in many technologies

4. Low-Noise GaAs HEMT technologies in Europe

5. Europe GaAs HEMTs (100nm or smaller)
OMMIC reaches G-band frequencies thanks to its 40nm GaAs process (D004MH).
UMS offers a GaAs low-noise 100nm process (PH10) suitable up to V-band
+LNF
INDUSTRIES
R&D labs
GaAs mHEMT (down to 20nm) technologies are available and have been presented in open literature.

6. Metamorphic HEMTs (high indium content in the channel, 70%)
OMMIC
Metamorphic HEMTs (high indium content in the channel, 70%)

7. OMMIC

8. Fraunhofer IAF
… and 20nm

9. Fraunhofer IAF
InxGa1-xAs mHEMT

10. Low-Noise Design Techniques

11. Design Techniques for LNAs
Very powerful derivations regarding the effect of feedback on the noise and gain of amplifiers were published by Haus and Alder back in the 60’s. These papers are not easily understood and are often ignored in current literature. They are the cornerstone of accurate low-noise amplifier synthesis.
Appropriate design methodologies leverage the transistor’s capabilities.
Finally, different design techniques apply to different operating frequencies.
millimetre-wave
Transistor gain is not enough to conceal the noise contribution on subsequent stages. The correct figure of merit for the transistor/technology is the noise measure, M.
Design effort is put upon obtaining low NF and adequate Gain. M takes into account both terms.
microwave
Very high transistor gain, enough to conceal the noise contribution from following stages
Design effort is put upon I/O match

12. Design Techniques for microwave LNAs
LNA designers often struggle to simultaneously satisfy gain, noise and I/O matching requirements. To this purpose a NOVEL DESIGN TECHNIQUE for multi stage low-noise amplifiers has been developed to obtain conjugate LNA I/O match.
LNA
Gain
Feedback Inductance
LNA interstage match
Feedback Inductance
Look for Author E. Limiti (et al.) in IEEExplore

13. Design Techniques for millimetre-wave LNAs
Optimum terminations in the source plane have been identified and discussed.
The effect of feedback has been carefully analyzed. Feedback eases the noise/gain trade-off, especially at higher frequencies.
The importance of Noise Measure (M) has been highlighted when designing millimetre-wave LNAs since the 1st stage’s FET available gain (Ge) is not enough to conceal the following stage’s noise contribution.
feedback reduces gain…
but also NFMIN is reduced.
….so MMIN is constant!
Look for Author E. Limiti (et al.) in IEEExplore

14. NF of GaAs in-house designed MMIC LNAs
Several LNAs have been designed in-house lately
In European Industrial Grade Technology…
OMMIC’s mHEMT GaAs process
70 nm
40 nm
EuMC
2017
EuMC
2008
MOTL
2018
Indicates Relative BW %
MOTL
2019
Min 15 % - Max 40%
JSSC
2010
Gain > 20dB
NF = 10*log(1+TN/T0)
Look for Author “E. Limiti” (et al.) in IEEExplore and Wiley Interscience

15. E-Band 71-86 GHz LNA with NF < 2.5dB
OMMIC D007IH 70 nm GaAs Industrial process
Four-stage, single ended MICROSTRIP
MMIC Size: 3.0 x 1.6 mm2
Gain 22dB - NF 2.3 dB TYP.
OP1dB +4dBm
OIP dBm

16. D-Band 125-155 GHz LNA with NF ≈ 5.0 dB
OMMIC D004IH 40 nm GaAs process
Four-stage, single ended COPLANAR
MMIC Size: 2.0 x 1.0 mm2
Gain 17dB - NF 5 dB typ.

17. Low-Noise Analysis, characterization and modelling capabilities

18. Analysis, characterization and modelling capabilities
I – Available instrumentation
II – Advanced measurement approaches
Calibrations
Test-benches
III – Model extraction
Passive devices
Active devices
IV – On-wafer non-linear measurements

19. Available instrumentation
4 Vector Network Analysers (HP 8510C GHz; Anritsu Lightning(37397B), GHz, extending to 110 GHz; Anritsu VectorStar (MS4640B) up to 125 GHz; Keysight E5061B, down to 1 Hz)
2 Spectrum Analyser (HP DC-40 GHz, Agilent PSA E4448A 3Hz-50GHz)
Noise Measurement System (HP8970B-HP8971C DC-26.5 GHz, with proprietary amplified SSB extension to 40 GHz; pre-amplifiers, LO frequency multipliers, isolators, waveguide switches, waveguide filters and noise sources to extend the hot/cold or cold-source SSB measurement range up to 75 GHz)
2 Elettromechanical Tuners (Focus GHz and 3-50 GHz)
Digital Sampling Oscilloscope (TekTronix up to 50 GHz)
I-V Pulsed Measurement System (GaAs Code)
Power Amplifier (AR GHz - 25 W)
Synthesised Sources (2 Anritsu MG3692A 2-20 GHz, HP 83640A up to 40 GHz, Agilent MXG N5183A up to 40 GHz, HP 83651A up to 50 GHz)
Vector Signal Source (Agilent E4438C 250 kHz-6 GHz)
Probe Stations (Cascade Microtech RF-1, SussMicrotec PM8, Cascade M150, all equipped with anti-vibrating tables)
Cryogenic Probe Station (down to 20 K, proprietary)
Test-fixtures (Wiltron, Agilent, …)

20. Calibrations Contribution of the access lines fully removed
Calibration approaches:
Commercial substrates vs custom substrates
SOLT vs TRL-like
Modeling at microwaves and up requires calibration on the same substrate as the devices
The accuracy to which the standards are known is of course low with custom calibration kits
On high-loss substrates, a combination of commercial and custom substrates may be required (two-tier) to extract Zc
Contribution of the access lines fully removed
Line propagation constant obtained as a by-product
Line characteristic impedance easily obtained also on low-loss substrates

21. (calibration comparison method)
Calibrations
The typical method for determining the characteristic impedance of the line standards in TRL-like calibrations is the “capacitance method” [1].
This is based, however, on the hypothesis that the substrate loss is negligible.
With lossy substrates, such as Silicon, the method fails: often this appears as over-unity magnitudes for reflection coefficients of passive (but highly reactive) loads.
The “calibration comparison method” comes in handy in these cases [2].
In this example (OMMIC D01GH, Run A) it is shown how the S11 of HEMT devices, which is highly reactive at low frequencies, may easily appear to feature over-unity magnitude when it is renormalized based on the capacitance method Zc.
This artifact is eliminated by using the calibration comparison method Zc.
S11
(capacitance method)
S11
(calibration comparison method)
Zc extraction
[1] Williams D. F. & Marks R. B., “Transmission line capacitance measurement.” IEEE Microwave and Guided Wave Letters, 1991, 1,
[2] Williams D. F., Arz U. & Grabinski H., “Characteristic-impedance measurement error on lossy substrates.” IEEE Microwave and Wireless Components Letters, 2001, 11,

22. Test-benches: Noise factor measurements
Typical noise test bench for on-wafer measurements
Term
Bias-Tee
DUT
Rcvr
Block 2b
Block 1
Block 2a
One-tier
Two-tier
SOLT
TRL
Can be eliminated by means of a full receiver calibration
Fixed or source pull

23. Test-benches: Noise characterization and modelling
Several methods of noise characterization available:
Y-factor [1]
Cold-source [1]
Source pull [1,2]
Source/load pull [3,4]
noise-temperature model
of the transistor
black-box characterization
of the whole noise parameter set
NF Y-factor measurement on the 4×35 µm device
at VDS = 5 V, JD = 250 mA/mm.
Notice the similarity in Gav and Gav,hc, with a possible exception around 31 GHz.
Cold-source measurement do not offer an analogous check.
[1] Limiti E., Ciccognani W. & Colangeli S., “Characterization and modeling of high-frequency active devices oriented to high-sensitivity subsystems design,” in Microwave de-embedding - From theory to applications, Elsevier, 2013,
[2] Lane R. Q., “The determination of device noise parameters,” Proceedings of the IEEE, 1969, 57,
[3] Ciccognani W., Colangeli S., Serino A., Longhi P. E. & Limiti E. “Generalized extraction of the noise parameters by means of Source- and Load-Pull noise power measurements,” IEEE Transactions on Microwave Theory and Techniques, 2018, 66,
[4] Randa J., “Comparison of noise-parameter measurement strategies: Simulation results for amplifiers,” 84th ARFTG Microwave Measurement Conference, 2014, 1-8

24. Test-benches: Source/load pull
Better conditioned system of equations resulting in reduced uncertainty in the estimation of Fmin and Rn.

25. Test-benches: SSB measurements at higher frequency (Q, V … W)
Q-band
Mixer: SAGE SFB-22-E2, 33 to 50 GHz, DC to 17 GHz IF, +3 dBm LO Power, WR-22 Waveguide, Q Band Externally Biased Balanced Mixer
LNA: LOW NOISE FACTORY LNF-LNR28_52WB, GHz
Low pass filter: SAGE SWF L1, 30 to 50 GHz, 40 dB Rejection from DC to 25 GHz and 56 to 100 GHz, Q Band, WR-22 Waveguide
WR22 DPDT switch: SAGE SWJ-22-TS, 33 to 50 GHz, 60 dB Isolation, WR-22 Waveguide, Q Band DPDT Motorized Switch
WR22/V transition: SAGE SWC-22VM-E1, WR-22 Waveguide to 1.85 mm V(M) Coax Adapter, End Launch
Bias tee: SHF BT65 (high voltage option), 1.85 mm V(M)-DCRF, 1.85 mm V(F)-RF
Frequency multiplier: QUINSTAR QPM-42052Q, passive multiplier, X2, input k-female output WR-22, UG-383
LO driver: Quinstar QPI-K0238JO KA-Fullband amplifier, input k-female, output k-male
Noise source: QUINSTAR QNS-FB15LQ, noise source with isolator

26. Model Extraction
Available modeling approaches:
Black-box vs equivalent circuit
Geometry-specific vs scalable
Measurements at lower frequencies can be performed, and the model extrapolated
Physical behavior guaranteed by construction
Possible fitting to extract the internal parameters, not to compute the external behavior
Scalability can be exploited during extraction to enhance model robustness: especially useful for active devices
Scalable models are required anyway

27. Model Extraction Standard equivalent circuit topology S11,4x50μm
CPW devices: no need for de-embedding via holes
μ-strip devices: EM simulation of the via holes
S11,4x50μm
Measurements up to 60 GHz
Models up to 110 GHz
S11,4x100μm

28. Active devices - OMMIC D01GH process
Noise temperature extraction
Γopt ΓS
[1] Colangeli S., Ciccognani W., Cleriti R, Palomba M. & Limiti E., “Optimization-based approach for scalable small-signal and noise model extraction of GaN-on-SiC HEMTs,” International Journal of Numerical Modelling: Electronic Networks, Devices and Fields, 2017, 30, e2135
[2] Pospieszalski M. W., “Modeling of noise parameters of MESFETs and MODFETs and their frequency and temperature dependence,” IEEE Transactions on Microwave Theory and Techniques, 1989, 37,
[3] Mokari M. E. & Patience W., “A new method of noise parameter calculation using direct matrix analysis,” IEEE Transactions on Circuits and Systems I: Fundamental Theory and Applications, 1992, 39, Rn
Closed-form least-squares fit of the 4×35 µm device noise factor at VDS = 5 V, JD  = 250 mA/mm:
Tg ≈ 314 K, Td ≈ 2798 K
NFmin ≈ 1.4 dB at 35 GHz
NFmin

29. Active devices - OMMIC D004IH process
Characterization and modelling activities performed within the framework of the TeraSCREEN and ULTRAWAVE projects.
Typical maximum gm: 80÷85 mS
DC measurements at a reference bias to assess the uniformity of the process and to select the most representative cells for the subsequent characterization and modelling activities.
Figures refer to measurements performed on a preliminary TeraSCREEN wafer

30. Active devices - OMMIC D004IH process
Characterization and modelling activities performed within the framework of the TeraSCREEN and ULTRAWAVE projects.
dB(S21)
Scattering parameters measurements at a reference bias to assess the uniformity of the process and to select the most representative cells for the subsequent characterization and modelling activities.
Figures refer to measurements performed on a preliminary TeraSCREEN wafer

31. Active devices - OMMIC D004IH process
Comparison between measurement and scalable model for a 2x20 µm DS15 devices
Bias ID max = 625 mA/mm ; VDS = 1 V; ID = 20% ID max = 50 mA
Characterization and modelling activities performed within the framework of the TeraSCREEN and ULTRAWAVE projects.
Fmeas vs Fmod
S11
S22
dB(S21)
NFmin, Rn

32. Conclusions
Europe offers research & production-grade GaAs mHEMTs technologies for millimeter-wave low-noise systems, comparable to overseas InP ones.
Technology alone does not solve any issue: device characterization and modelling, appropriate design methodologies are key elements.

33. E.E.Dept. head, University of Rome “Tor Vergata”, Rome, Italy
HEMTs in Europe (GaAs HEMT low-noise technologies, design techniques, characterization and modeling)
Ernesto Limiti
E.E.Dept. head, University of Rome “Tor Vergata”, Rome, Italy

34. References Low-Noise Amplifier Design Techniques
Ciccognani, W., Longhi, P.E., Colangeli, S., Limiti, E., “Constant mismatch circles and application to low-noise microwave amplifier design”, IEEE Transactions on Microwave Theory and Techniques, 61(12), , pp , 2013.
Ciccognani, W., Colangeli, S., Limiti, E., Longhi, P. “Noise measure-based design methodology for simultaneously matched multi-stage low-noise amplifiers”, IET Circuits, Devices and Systems, 6(1), pp , 2012.
Colangeli, S., Ciccognani, W., Salvucci, A., Limiti, E., “Deterministic design of simultaneously matched, two-stage low-noise amplifiers”, Asia-Pacific Microwave Conference Proceedings, pp , 2018.
Low-Noise Active Devices Characterization & Modeling
Ciccognani, W., Colangeli, S., Serino, A., Longhi, P.E., Limiti, E., “Generalized Extraction of the Noise Parameters by Means of Source-and Load-Pull Noise Power Measurements” IEEE Transactions on Microwave Theory and Techniques, 66(5), pp , 2018.
Colangeli, S., Ciccognani, W., Palomba, M., Limiti, E., “Automated extraction of device noise parameters based on multi-frequency, source-pull data”, International Journal of Microwave and Wireless Technologies, 6(1), pp , 2014.
Cleriti, R., Ciccognani, W., Colangeli, S., (...), Frijlink, P., Renvoisé, M., “Characterization and modelling of 40 nm mHEMT process up to 110 GHz”, 11th European Microwave Integrated Circuits Conference, pp , 2016
Cleriti, R., Colangeli, S., Ciccognani, W., Palomba, M., Limiti, E., “Cold-source cryogenic characterization and modeling of a mHEMT process”, European Microwave Week, pp , 2015.

35. Reference Millimetre-wave GaAs LNAs
Ciccognani, W., Colangeli, S., Longhi, P.E., Limiti, E., “Design of a MMIC low-noise amplifier in industrial gallium arsenide technology for E-band 5G transceivers”, Microwave and Optical Technology Letters 61(1), pp , 2019.
Ciccognani, W., Longhi, P.E., Colangeli, S., Limiti, E. “Q/V band LNA for satellite on-board space applications using a 70 nanometers GaAs mHEMT commercial technology”, Microwave and Optical Technology Letters 60(9), pp , 2018.
Cleriti, R., Ciccognani, W., Colangeli, S., et al.., “D-band LNA using a 40-nm GaAs mHEMT technology”, 12th European Microwave Integrated Circuits Conference, pp , 2017.
Ciccognani, W., Colangeli, S., Limiti, E., Scucchia, L., “Millimeter wave low noise amplifier for satellite and radio-astronomy applications”, IEEE 1st AESS European Conference on Satellite Telecommunications, ESTEL 2012.
Ciccognani, W., Limiti, E., Longhi, P.E., Renvoisè, M., “MMIC LNAs for radioastronomy applications using advanced industrial 70 nm metamorphic technology” IEEE Journal of Solid-State Circuits, 45(10), pp , 2010.
Ciccognani, W., Giannini, F., Limiti, E., Longhi, P.E., “Full W-band high-gain LNA in mHEMT mmic technology” European Microwave Integrated Circuit Conference, EuMIC 2008, pp , 2008.